Method of manufacturing stockings from two-component filaments



United States Patent 3,271,837 METHOD OF MANUFAOTURKNG STOCKINGS FROM TWO-COMPONENT FHLAMENTS Tin Yam Au and Earl Herbert Olson, Wilmington, Del, assignors to E. 1. du Pont de Nemours and Company, Wilmington, Del, a corporation of Delaware No Drawing. Filed Sept. 25, 1964, Ser. No. 399,401

3 Claims. (Cl. 28-74) This application is a continuation-in-part of United States application 249,324 to Au and Olson, filed January 4, 1963, now abandoned, which in turn is a continuationin-part of United States application 132,449 to Olson, filed August 18, 1961, now abandoned.

This invention relates to textiles, and more particularly to a novel process of relaxed steaming for greige knit stockings.

Seamless stockings are generally considered to have poorer fit and comfort characteristics than can be achieved with full-fashioned stockings although the seamless are preferred for cosmetic reasons and because with seamless there is no need to keep a straight seam. Seamless knitting machines depend on stitch tightening to shape the seamless stockings in the ankle region. Additional shaping is required to achieve commercially acceptable seamless stockings and is accomplished by thermal shrinking and setting on a flat boarding-form in hot moist air at about 240270 F. Nevertheless;after periods of sustained wear, such stockings experience fabric fatigue and loosening, or bagging. One attempt to solve the problem of poor fit is to produce stretch stockings from yarn that has been crimped by being passed over a heated surface. However, this crimping does not produce uniform filament qualities. When stockings constructed with a nylon two-component crimpable filament are shaped by the conventional thermal shrinking and board-setting in hot moist air at about 260 F., the stress retention against the wearers legs, particularly in the knee and ankle area, is not significantly different from the stress retention accomplished with conventional polyhexamethylene adipamide stockings similarly processed. When the wearer adjusts a stocking to attain comfortable fit, stress is placed and retained on the stocking. If stress retention is low the stocking loosens or bags.

The principal objective of this invention is to provide a process for finishing stockings that will remain snug, particularly in the knee and ankle area, even after periods of sustained wear.

Another objective is to provide a superior process of finishing stockings that have been knit from a nylon twocomponent filament.

Other objectives will appear hereinafter.

These objectives are accomplished by steaming relaxed greige stockings knit from a nylon two-component crimpable filament whose two components are of fiber-forming molecular weight and have dissimilar shrinkage values, said steamig being carried out within the range of from about 215 F. to about 250 F. with substantially saturated steam. Such stockings are referred to hereinafter as relaxed-steamed.

The filaments used to knit the stockings of this invention are monofilaments comprised of two components. The two components, which are both of fiber-forming molecular weight and have dissimilar shrinkage properties, occupy discrete areas, as opposed to a random intermixture, in and on the monofilaments. Conventional bicomponent filaments such as sheath-core, side-by-side, and combinations thereof are suitable in this invention. Each component may, in turn, be composed of a single polyamide, or a blend of polyamides.

When greige Stockings knit from two-component fila- 3,271,837 Patented Sept. 13, 1966 ments of nylon (each component being of fiber-forming molecular weight) are relaxed-steamed in accordance with the process of this invention, a novel crimp develops in the filament. This crimp has high recovery property and, therefore, the stockings retain most of their stress bearing capacity even after being repeatedly strained. When relaxed-steamed at temperatures below 215 P. such stockings exhibit insufficient yarn crimp while upon being relaxed-steamed at temperatures above 250 F shrinkage is excessive. If relaxing is effected with dry heat (rather than steam) in the range of from about 215 F. to about 250 F. there is poor crimp development, the stockings have shiny finish, and dyeing to the darker shades is difficult to accomplish. When greige stockings knit from conventional polyhexamethylene adipamide filaments are relaxed-steamed at temperatures greater than about 215 F., the shrinkage is so excessive that the stockings are unacceptable. In the conventional thermal shrinking and setting process the flat boarding is used to prevent excessive shrink-age.

It should be noted that the temperature of the steam supply for the process of this invention needs to be more than 215 F. in order to make-up for the unavoidable heat loss through the walls of the apparatus wherein the steaming takes place. For the same reason, since the maximum steaming temperature is 250 F., the steam supply must then be slightly more than 250 F. Therefore the range 215-250" F. is for the steaming process, and not for the steam. supply.

The following examples are cited to illustrate the invention and are not intended to limit the scope thereof in any manner.

In these examples, stress retention is measured on an Instron machine. First, the stocking is stretched longitudinally to simulate garter tension. Then, a transverse strain is placed on the stocking by stretching it in the knee area, so that the stocking width at the stretched zone is equivalent to a circumference of 14'. This transverse strain is applied by means of a magnetic clamp. Next, the tension on the stocking is increased so that the width at the stretched zone is equivalent to a circumference of 15". Finally, the tension is released so that the zone returns to the 14" equivalent. These three continuous steps are repeated 10 times. The stress on the first stretching to 14" and the stress on the final stretching to 14" are measured. Percent stress retention equals 100 times (final stress at the tenth 14" strain) (original stress at the first 14" strain) When stress retention in the ankle region is to be measured, the same test is made except that the strain is first 8", then 9" and finally 8"; each dimenion being as above, the equivalent to the specified circumference.

The expression relative viscosity as used herein, signifies the ratio of the flow time in a viscosimeter of a polymer solution containing 8.2% i0.2% by weight of polymer in a solvent, relative to the flow time of the solvent by itself. Measurements of relative viscosities given in the example were made with the following solution: 5.5 g. of a polyamide in 50 ml. of formic acid at 25 C.

EXAMPLE I filament yarn. The knitting machine is a single feed, 400 needle, 3% cylinder machine with the following program linkage:

408 welt courses 60 shadow welt courses 840 leg courses 528 ankle courses 360 foot courses 180 x 180 heel courses 204- x 216 toe courses and with greige stretch characteristics as follows:

Welt stretch 14" Leg stretch 13 Ankle and foot stretch 10" These greige stockings are relaxedsteamed by being laid down unfolded on an open nylon-mesh-covered metal tray located in a steam chest into which is fed saturated steam until the temperature of the chest at atmospheric pressure is approximately 215 F. at which conditions the stockings are kept for 30 minutes. The stockings are then removed, dumped in a mesh bag, and the bag placed into a rotary stocking-dyeing machine where these stockings are dyed. These dyed stockings are then boarded on a flat form and kept in a steam chest at 245 F. for 45 seconds. These stockings are then removed from the boarding forms for inspection and testing. It is observed that the monofilaments are well crimped, and that the stockings fit a large variety of leg shapes without wrinkling or bagging even after pr-olonged wear. Comfortable tension levels, particularly at the ankle area are retained during each period of wear. The stockings have a dry, lively hand, give a matte appearance, give a soft feel to the leg, and have no pattern effect either on or off the wearer.

An additional six pairs of test stockings (identified hereinafter as T stockings) are knit in the same manner and from the same yarn employed in knitting the T stockings. However the T stockings are relaxedsteamed at 245 F. for 5 minutes while hanging free in a steam chest and then dyed and boarded in the manner and under the conditions employed in dyeing and boarding the T stockings. The T stockings are similar to the T stockings except that the T pairs are of a miniature style which has small dimensions in the relaxed condition. Such stockings comfortably fit a wide variety of leg dimensions.

Six pairs of test stockings (identified hereinafter as T stockings) are knit from a sheath-core two-oomponent side-by-side bright filament comprising polyhexamethylene adipamide having a relative viscosity of 52 on one side, a copolymer [relative viscosity of 56] of polyhexamethylene adipamide with polyhexamethylene sebacamide on the other side, and a thin sheath of polyhexamethylene adipamide having a relative viscosity of 52 surrounding both interior components (a process for preparing such yarns is described and claimed in a United States patent application Serial No. 248,640, filed December 31, 1962) in the same manner employed in knitting the T stockings. The T stockings are rel-axed-steamed, dyed and boarded following the procedure used in preparing the T stockings. The T stockings exhibit fit, comfort, feel and appearance properties similar to those cited for the T stockings.

For comparison a series of control stockings is prepared. The preparation and identity of the various samples upon which stress retention determinations are made follows. The results of the cyclic deformation tests appear in Tables 1 and 2.

Six pairs of ladies size 9 /2l0, semi-conventional style, medium-length, seamless control stockings (identified hereinafter as C stockings) are knit with conventional, single-component polyhexamethylene adipamide [relative viscosity of 52] bright filaments. When the greige control stockings are relaxed-steamed as are the T or T stockings, they shrink significantly; thereafter they are dyed and then boarded on a flat form in the manner and under the conditions employed in dyeing and boarding the T stockings.

Six pairs of ladies medium length, seamless control stockings (identified hereinafter as C stockings) in the size range 9 /2lO, are knit with the same type filaments as used for the C stockings. These greige stockings are shaped by thermal shrinking and setting on a flat boarding-form in hot moist air at about 260 P. Then these stockings are dyed and reboarded in the manner and under the conditions employed in dyeing and boarding the T stockings. The same procedural steps used in preparing the C stockings are followed to prepare other control stockings (identified hereinafter as C stockings) except that the yarn employed is the same as that used in making the T stockings. Other comparative control stockings (identified hereinafter as C stockings) are similar to the C stockings except for a relaxed, aqueous treatment at 210 F. prior to the flat-boarding in hot moist air.

Table I After After Stockings Greige 1 relaxedboarding 1 steaming 1 1 Percent stress retention in knee area.

Table II Stockings: A-flter boarding 1 C 31-42 C 38-45 C 35-50 T 65-70 T -75 T 65-70 1 Percent stress retention in ankle region.

The percent stress-retention range specified in Table II represents the observed variations among individual stockings.

EXAMPLE II A side-by-side, two-component, 16.0-denier, monofilament yarn wherein one component is polyhexamethylene adipamide [relative viscosity of 52] and the other component is a 50/50 copolymer [relative viscosity of 56] of polyhexamethylene adipamide and polyhexamethylene sebacamide, is knit into Womens stockings of 10 /2 knit size and 35-inch knit length. Thereafter the welt of each greige stocking is clamped to a steel board and placed in a closed oven with the stocking hanging loosely from the board. Five pounds per square inch (gauge) steam (about 227 F.) is applied to the oven for 2 minutes. These test stockings are then finished and dyed using conventional steps. Control stockings are knit, finished and dyed identically to these test stockings except that the control stockings are subjected to a 10-minute boil-01f (as taught in US. Patent No. 2,333,160) instead of the relaxed-steaming in the closed oven. The test stockings of this example are substantially better fitting and have a more pleasing finish than their controls.

Preferred results for the miniature style of hosiery relaxed-steamed according to this invention are achieved within the temperature range 240 F.245 F. while for semi-conventional style medium-length sizes preferred results are achieved within the range 215 225 F.

According to this invention, relaxed steaming for the stockings is to be effected with saturated dry steam. Optimum crimp is not developed if supplementary heating is used.

It should be noted that the stress retention in the stockings, steam-relaxed according to the present invention, maintains comfortable tensions against the users legs during the entire period of wear. The superior fit and comfort sensations achieved with these stockings are due to the acquired ability of the stockings to exert suitable forces against the wearers legs for a wide range of leg dimensions, and to maintain these forces during the time the stockings are Worn. The maintenance of suitable forces against the wearers legs is the key element in providing superior levels of fit and comfort as well as in eliminating the bagging and wrinkling which mar the appearance of both conventional seamless and full-fashioned stockings.

This process also is useful for finishing full-fashioned, tubular, and run-resist stockings. Full-fashioned stockings accomplish good fit because they are tailored and are knit in a very large number of sizes. When fullfashioned stockings are knit from nylon two-component crimpable filaments wherein the components are of fiberforming molecular weight, and then relaxed-steamed according to this invention, the crimp developed improves the fit to such an extent that fewer sizes are needed.

Tubular stockings are those knit so that the foot and heel are continuations of the ankle courses. Therefore, in the absence of tailoring and special stocking construction, the thermal shrinking needed on a flat board to approach an acceptable shaping and fit is much greater for a tubular stocking. Consequently, tubular stockings bag to a greater extent, and more quickly than do conventional seamless stockings. Tubular stockings that are knit from the two-component crimpable nylon filaments and then relaxed-steamed according to this invention fit better and possess improved shape.

Run-resist stockings have a lack of compliance which is intrinsic to their knit structure and therefore do not have optimum shape and fit. If the run-resist stockings are knit from the nylon two-component crimpable filaments, and then relaxed-steamed according to this invention, the resultant novel crimp gives the stockings the compliance which makes them more useful and durable.

In selecting a temperature for relaxed-steaming, it should be noted that the higher the temperature, the greater the crimp development; however, the relaxed size of the finished stockings diminishes as temperature increases. Steaming time ranges from one to sixty minutes, depending on the quantity of stockings being processed in one batch, the larger number of stockings being processed for the longer time.

For this invention, final boarding after dyeing is carried out conventionally which is within the temperature range from 230 F. to 255 F., and for from 30 to 90 seconds. The two-component filaments used may be simply side-by-side or side-by-side with surrounding sheath and they are crimpable because of the different shrinkage potential of the two components. Combinations of polymers which are useful for this invention form filaments of polyhexamethylene adipamide along with a copolymer of polyhexamethylene adipamide and a polyamide selected from the group consisting of polyhexamethylene sebacamide, polyhexamethylene isophthalamide, polyhexamethylene suberamide and polyhexamethylene dodecanediamide.

It should be noted that the viscosities of the components of the filaments for these test stockings are well above the minimum required for commercial spinning of fibers. In terms of relative viscosity, the characterization of molecular weight, 28 is the minimum relative viscosity which can be used for commercial production of fibers.

The novel process of this invention provides a novel stocking with excellent fit and comfort characteristics because of the stockings unexpected stress retention. But the process is restricted to stockings knit with filaments comprised of fiber-forming components. These fiberforming components must be extruded from polymer of fiber-forming molecular weight in order to avoid processing difliculties and to provide filaments which have the crimpability that results in the unexpected stress retention. In side-by-side extrusion the use of a low molecular weight component leads to bending of the filaments as they emerge from the spinneret orifice, and commercial operability is not obtained. In either side-by-side or sheath-core extrusion it is found that the surface tensions of the two molten polymers must be approximately equal to obtain filaments having the desired high crimping force. For practical production of hosiery filaments, one component must have a relative viscosity of at least about 35 at extrusion in order to avoid serious processing difficulties. Preferably, any two components differ in relative viscosity by not more than 10 units.

Many other equivalent modifications will be apparent to those skilled in the art, and, therefore, this invention is not intended to be limited except as indicated in the appended claims.

What is claimed is:

1. A process for manufacturing a stocking knit from a nylon two-component crimpable filament whose two components are of fiber-forming molecular weight and have dissimilar shrinkage values, comprising in order the steps of (1) knitting a stocking from the said two component filament, (2) relax-steaming said stocking at a temperature of from about 215 F. to 250 F. with substantially saturated steam for a period of at least about one minute, (3) dyeing the said stocking and (4) postboarding the said stocking in a steam chest at a temperature of from about 230 F. to 255 F. for a period of at least about 30 seconds, whereby the stocking exhibits a stress retention of at least about 60% in the knee and ankle region subsequent to said postboarding.

2. The process of claim 1 wherein the said filament is a side-by-side two component filament wherein one component is polyhexamethylene adipamide and the other component is a copolymer of polyhexamethylene adipamide and polyhexamethylene sebacamide, each of said components being of fiber-forming molecular weight.

3. The process of claim 1 wherein the said filament is a side by-side with surrounding sheath, two-component filament wherein one component and the sheath are polyhexamethylene adipamide and the other component is a copolymer of polyhexamethylene adipamide and polyhexamethylene sebacamide, each of said components being of fiber-forming molecular weight.

References Cited by the Examiner UNITED STATES PATENTS 2,157,119 5/1939 Miles 2874 2,333,160 11/1943 Dunn 223-76 X 2,420,960 5/1947 Larkin 2874 2,931,091 4/1960 Breen. 2,987,797 6/ 1961 Breen. 3,038,235 6/1962 Zimmerman 161-175 X 3,038,236 6/ 1962 Breen.

3,069,883 12/1962 Burleson et a1. 66-178 3,077,757 2/1963 Bobo et al. 66178 FOREIGN PATENTS 791,960 3/1958 Great Britain.

ROBERT R. MACKEY, Primary Examiner. DONALD W. PARKER, Examiner. 

1. A PROCESS FOR MANUFACTUING A STOCKING KNIT FROM A NYLON TWO COMPONENT CROMPABLE FILAMENT WHOSE TWO COMPONENTS ARE OF FIBER-FORMING MOLECULAR WEIGHT AND HAVE DISSIMILAR SHRINKAGE VALUES, COMPRISING IN ORDER THE STEPS OF (1) KNITTING A STOCKING FROM THE SAID TWO COMPONENT FILAMENT, (2) RELAX-STEAMING SAID STOCKING AT A TEMPERATURE OF FROM ABOUT 215*F. TO 250*F. WITH SUBSTANTIALLY SATURATED STEAM FOR A PERIOD OF AT LEAST ABOUT ONE MINUTE, (3) DYEING THE SAID STOCKING AND (4) POSTBOARDING THE SAID STOCKING IN A STEAM CHEST AT A TEMPERATURE OF FROM ABOUT 230*F. TO 255*V. FOR A PERIOD OF AT LEAST ABOUT 30 SECONDS, WHEREBY THE STOCKING EXHIBITS A STRESS RETENTION OF AT LEAST ABOUT 60% IN THE KNEE AND ANKLE REGION SUBSEQUENT TO SAID POSTBOARDING. 